1. Field of the Invention
The present invention relates to a particle size distribution measuring apparatus, and more particularly to an array detector used in the measuring apparatus of a configuration to maximize production yield and a manufacturing method for forming a plurality of array detectors.
2. Description of Related Art
A particle size distribution measuring apparatus has been provided with a limited array detector having a plurality of light detecting elements (devices) for detecting an intensity of scattering light at various scattering angles when a laser beam from a laser beam source is irradiated onto dispersed particles.
FIG. 4 schematically shows the principal parts of a conventional particle size distribution measuring apparatus. A circulating type cell 1 (flow cell) comprising a transparent container, receive a sample solution 2 prepared by dispersing a particle group of a sample target for measurement in a proper dispersion medium. A laser beam source section 3 is located on one side (rear side) of the cell 1. The laser beam source section 3 is composed of a laser beam source 5 comprising a He-Ne laser emitting a parallel laser beam 4, towards mirrors 6 and 7 for changing a traveling direction of the laser beam 4 by an angle of 90.degree., and a beam expander 8 for properly enlarging the parallel laser beam 4 in a light (beam) flux direction.
A collective (condenser) lens 9 is located on the other side (front side) of the cell 1, and a ring-like array detector 10 is arranged on a focal position. As shown in FIG. 5, the array detector 10 comprises a transmitted light detecting element 11 which is formed on a position corresponding to an optical axis of the collective lens 9, and a scattering light detecting element group 12 for detecting scattered light 4A. The scattering light detecting group 12 comprises a plurality of circular-arc scattering light receiving elements 12, 12b, . . . 12n, which are formed coaxially with the transmitted light detecting element 11 so as to have a wider width as they are positioned remote from the transmitted light detecting element 11. Incidentally, a reference numeral 13 denotes an isolation gap between detecting elements. The aforesaid array detector 10 receives the light scattered/diffracted at a relatively small angle of the laser beam 4A as it is diffracted or scattered by the particles in the cell 1 for various scattering angles, and then, measures their light intensity. The transmitted light detecting element 11 is used for adjusting a position optical axis and for measuring a concentration of the sample solution 2.
A reference numeral 14 denotes a multiplexor which successively captures an output (scattering light intensity signal) of the array detector 10, and successively transmits it to an A/D converter 15, and a computer 16 which functions as a processor to which an output of the A/D converter 15 is inputted. The computer 16 stores a program for processing the output of the array detector, converted into a digital signal, on the basis of a Fraunhofer diffraction theory or a Mie scattering theory, and for determining a particle size distribution of the particle group. A reference numeral 17 denotes a color display for displaying the processed results or the like.
In the aforesaid particle size distribution measuring apparatus, where the sample solution 2 is supplied to the cell 1, and the laser beam 4 from the laser beam source is irradiated to the sample cell 1, the laser beam 4 is diffracted or scattered by the particles in the cell 1. A diffracted or scattered laser beam 4A is incident upon the array detector 10 by means of the collective lens 9, and then, each output from the scattering light receiving elements 12a, 12b . . . 12n constituting the array detector 10, is amplified by means of a pre-amplifier (not shown), and thereafter, is inputted to the multiplexor 14.
In the multiplexor 14, a light intensity data for each scattering angle obtained by the array detector 10, that is, an analog electric signal is successively captured in a predetermined order. The analog electric signal captured by the multiplexor 14 is made into a serial signal, and then, is successively converted into a digital signal, and further, is inputted to the computer 16. The computer 16 processes the light intensity data for each scattering angle obtained by the array detector 10 on the basis of a Fraunhofer diffraction theory or a Mie scattering theory, and thus, determines a particle size distribution of the particle in the sample solution 2. Then, the result is displayed on the color display 17, or is stored in a memory device (not shown).
The aforesaid array detector 10 is manufactured by cutting a wafer into a predetermined shape. In the conventional case, an open (sector) angle of each element 12a to 12n constituting the scattering light detecting element group 12 has been set to a fixed angle, for example, an angle of 90.degree.. For this reason, the array detector 10 has the following problems. More specifically, in the array detector 10, there is a need to mutually make equal the scattering light detecting characteristics of the scattering light detecting elements 12a to 12n. For this reason, as shown in FIG. 5, the array detector 10 is formed in a manner that a dimension of the respective scattering light detecting elements 12a to 12n is gradually increased in its radius direction and circumferential direction from the transmitted light detecting element 11, and also, an area thereof is increased in an exponential function. In this case, if each open (sector) angle of the scattering light detecting elements 12a to 12n is held constant, as a radius distance from the transmitted light detecting element 11 gradually becomes larger, an area of each effective light collection portion (portion shown by a symbol "a" in FIG. 5) of the scattering light detecting elements 12a to 12n is increased. For this reason, the array detector 10 is required to be of a relatively large size, and also, any equipment for holding the array detector 10 becomes large, as a result, the particle size distribution measuring apparatus will be of a large size.
Moreover, the number of the array detectors 10 capable of being manufactured from a single wafer 18 is four (4) as shown in FIG. 5, in the case where the detector element sector angle is 90.degree.. Therefore, the number of array detectors 10 capable of being manufactured from a single wafer is limited as number; for this reason, there is an increase in cost, and as a result, the particle size distribution measuring apparatus becomes expensive.
Examples of conventional array detectors can be seen in U.S. Pat. No. 5,164,787 and U.S. Pat. No. 5,185,641.
The prior art is still seeking improved and cost efficient array detectors.